Mobile Device Assisted Coordinated Multipoint Transmission and Reception

ABSTRACT

Idle mobile devices are used as cooperating devices to support coordinated multipoint transmission and reception for uplink and downlink communications between a primary mobile device and its serving base station. For uplink communications, the cooperating mobile devices receive the uplink transmission from the primary mobile device and retransmit the received data signal to the serving base station for the primary mobile device. For downlink communications, the cooperating mobile devices receive the downlink transmission from the serving base station and retransmit the received data signal to the primary mobile device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application No.13/723,841, filed Dec. 21, 2012, which is entitled “MOBILE DEVICEASSISTED COORDINATED MULTIPOINT TRANSMISSION AND RECEPTION,” and whichis hereby incorporated by reference as if fully set forth herein.

TECHNICAL FIELD

The present invention relates generally to coordinated multipoint (CoMP)transmission and reception in a wireless communication network and, moreparticularly, to methods and apparatus for implementing mobile deviceassisted CoMP transmission and reception in which mobile devicesfunction as CoMP nodes for other mobile devices.

BACKGROUND

The phenomenal growth in demand for wireless communications has putpersistent pressure on wireless network operators to improve thecapacity of their communication networks. To improve the spectralefficiency of these networks, scarce radio resources have to be reusedaggressively in neighboring cells. As a result, inter-cell interferencehas become a main source of signal disturbance, limiting not only theservice quality to users at the cell edges, but also the overall systemthroughput.

Coordinated Multi-Point (CoMP) reception in the uplink is one techniquebeing considered for mitigating inter-cell interference in InternationalMobile Telecommunications (IMT) Advanced systems. For the uplink (UL),CoMP reception differs from reception in a conventional system in thatuplink signals are received at multiple, geographically dispersed basestations, and then sent across backhaul communication links to a commonlocation for joint processing (e.g., to the serving base station). Ineffect, this architecture forms a “super-cell,” called a CoMP cell,where uplink signals that would have been treated by a conventional cellas inter-cell interference are instead treated by the CoMP cell asdesired signals. The mitigation in inter-cell interference is expectedto significantly improve system performance, especially for users nearthe edge of a conventional cell.

Sending the received uplink signals across backhaul communication linksfor joint processing, however, can require significant and potentiallyprohibitive backhaul bandwidth. For many transmissions, the cooperatingnode is under a stringent time deadline to deliver the CoMP payload tothe serving node for processing. For example, it is desirable that theuplink signals received by a cooperating node be processed and the CoMPpayload delivered to the serving node within the time deadline forHybrid Automatic Repeat Request (HARQ). In Long Term Evolution (LTE)systems, the HARQ timing is typically set to 4 ms, so that the HARQprocess can assist in exploiting the short term behavior of the wirelesschannel. Usual solutions deliver the CoMP payload with a latency of lessthan 500 μs, which allows the payload to be useful to the serving cellwithin the HARQ deadline. The requirement for low latencies drives thepeak data rates on the backhaul and requires very high bandwidth on thebackhaul.

The synchronous nature of the cells also contributes to the high peakdata rates. Because the transmission in all cells is synchronous, theCoMP payloads from many different nodes may be transmitted over thebackhaul at the same time causing peak congestion. The averageutilization of the links will be low, while the short peaks drive thebandwidth requirement and link costs.

Processing loads for processing the CoMP payloads is another area ofconcern. Solutions that minimize the processing load for CoMP operationsare advantageous.

SUMMARY

The present invention takes advantage of the distributed nature ofmobile devices and employs device-to-device (D2D) communications toenhance performance of both uplink and downlink CoMP in a wirelesscommunication network.

In exemplary embodiments of the invention, idle mobile devices are usedas cooperating devices to support coordinated multipoint transmissionand reception for uplink and downlink communications between a mobiledevice and its serving base station. In addition to neighboring basestations, a mobile device can join a CoMP session. For uplinkcommunications, the cooperating mobile devices receive the uplinktransmission from the supported mobile device and retransmit thereceived data signal to the serving base station for the supportedmobile device. For downlink communications, the cooperating mobiledevices receive the downlink transmission from the serving base stationand retransmit the received data signal to the supported mobile device.

Exemplary embodiments of the invention comprise methods implemented by acooperating mobile device in a wireless communication network forsupporting coordinated multipoint transmission and reception for aprimary mobile device. In one exemplary method, the cooperating mobiledevice joins a coordinating set for the primary mobile device. Thecoordinating set includes a serving base station for the primary mobiledevice. While a member of the coordinating set, the cooperating mobiledevice receives a data signal transmitted from either the primary mobiledevice to the serving base station, or from the serving base station tothe primary mobile device. The cooperating mobile device retransmits thedata signal to either the serving base station for uplink communicators,or to the primary mobile device for downlink communications.

Other embodiments of the invention comprise a cooperating mobile devicein a wireless communication network for supporting coordinatedmultipoint transmission and reception for a primary mobile device. Thecooperating mobile device comprises a transceiver circuit configured totransmit and receive signals over a wireless communication channel, anda processing circuit including a coordinated multipoint control circuit.The processing circuit is configured to join a coordinating set for theprimary mobile device. The coordinating set includes a serving basestation for the primary mobile device. The processing circuit isconfigured to receive, as a member of the coordinating set for theprimary mobile device, a data signal transmitted from either the primarymobile device to the serving base station, or from the serving basestation to the primary mobile device. The processing circuit is furtherconfigured to retransmit, as a member of the coordinating set for theprimary mobile device, the data signal to the serving base station foruplink communications, or to the primary mobile device for downlinkcommunications.

Other embodiments of the invention comprise methods implemented by aserving base station in a wireless communication network for supportingcoordinated multipoint reception for a primary mobile device. In oneexemplary method, the serving base station receives a first data signaltransmitted by the primary mobile device, and receives a second datasignal as retransmitted by a cooperating mobile device in a coordinatingset for the primary mobile device. The second data signal comprises aretransmission of the first data signal. The serving base stationfurther combines the first and second data signals to produce a combineddata signal.

Other embodiments of the invention comprise a serving base station in awireless communication network for supporting coordinated multipointtransmission and reception for a primary mobile device. The serving basestation comprises a transceiver circuit configured to transmit andreceive signals over a wireless communication channel, and a processingcircuit including a coordinated multipoint control circuit. Theprocessing circuit is configured to receive a first copy of a datasignal transmitted by a primary mobile device, and to receive a seconddata signal as retransmitted by a cooperating mobile device in acoordinating set for the primary mobile device. The second data signalcomprises a retransmission of the first data signal. The processingcircuit is further configured to combine the first and second datasignals to produce a combined data signal.

The present invention improves network capacity and throughput by takingadvantage of the distributed nature of mobile devices and employingdevice-to-device (D2D) communications. In addition to improving capacityand throughput, the present invention improves interferencecoordination, and eliminates coverage holes for mobile devices in poorcoverage areas. Using mobile devices as participants in a CoMP sessioncan also reduce the bandwidth requirements for backhaul communicationsbetween neighboring base stations, as well as processing loads on thebase stations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication network implementing mobiledevice assisted Coordinated Multipoint Reception (CoMP).

FIG. 2 is a flow diagram illustrating coordinated multipoint receptionfor uplink communications according to one embodiment.

FIG. 3 is a flow diagram illustrating coordinated multipoint receptionfor uplink communications according to one embodiment.

FIG. 4 is a flow diagram illustrating coordinated multipoint receptionfor downlink communications according to one embodiment.

FIG. 5 is a flow diagram illustrating coordinated multipoint receptionfor downlink communications according to one embodiment.

FIG. 6 illustrates an exemplary method implemented by a cooperatingmobile device in a coordination set for supporting coordinatedmultipoint transmission and reception by a primary mobile device.

FIG. 7 illustrates an exemplary method implemented by a base station forselecting one or more cooperating devices for a coordinating set for aprimary mobile device.

FIG. 8 illustrates an exemplary method implemented by a cooperatingmobile device for joining a coordinating set for a primary mobiledevice.

FIG. 9 illustrates another exemplary method implemented by a cooperatingmobile device for joining a coordinating set for a primary mobiledevice.

FIG. 10 illustrates the main functional components of communicationdevice implementing coordinated multipoint transmission and reception.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates a coordinatedmultipoint (CoMP) system 10 according to one exemplary embodiment of theinvention. The CoMP system 10 comprises a plurality of geographicallydispersed base stations 12 providing service to mobile devices 14 inrespective cells 16 of the CoMP system 10. In FIG. 1, two base stations12 and four mobile devices 14 are illustrated. In LTE, a base station isreferred to as an Evolved Node B (eNodeB or eNB) and a mobile device isreferred to as a user equipment (UE). The base stations 12 are denotedBS1 and BS2, respectively. The mobile devices 14 are denoted UE1, UE2,UE3 and UE4 respectively. BS1 is the serving base station 12 for UE1,UE2 and UE3, while BS2 is the serving base station 12 for UE4. Theuplink signals from the mobile devices 14 to the base stations 12 aredenoted as s_(ij) where i indicates the mobile device 14 and j indicatesthe base station 12.

In a CoMP system 10, the uplink signals transmitted from the mobiledevices 14 are typically received by multiple base stations 12 within acoordinating set, also referred to herein as a CoMP set. For purposes ofthis application, the term “coordinating base station 12” refers to anybase station 12 in a coordinating set (i.e. the “CoMP set”) thatcontrols the CoMP session. The term “cooperating node” refers to eithera base station 20 (i.e., cooperating base station 20) or mobile device14 (cooperating mobile device 14) in the cooperating set. For a givenmobile device 14, the coordinating set typically includes a coordinatingor serving base station 12 and at least one other cooperating node,which may be a cooperating base station 12 or cooperating mobile device14.

In the example shown in FIG. 1, the CoMP set for both UE1 and UE2includes BS1 and BS2. BS1 receives uplink signals s₁₁ and s₄₁ from UE1and UE4 respectively. BS1 may send the received signal s₄₁ over abackhaul link to BS2 for processing by BS2. BS2 receives uplink signalss₁₂ and s₄₂ from UE1 and UE4 respectively. BS2 may send the receivedsignal s₁₂ over a backhaul ink to BS1 for processing by BS1.

UE1 is part of a local cluster 18 of mobile devices 14 that includes UE2and UE3. UE3 is transmitting uplink signal s₃₁ to BS1. UE2 is idle. Amobile device 14 may be part or more than one local cluster 18.

In exemplary embodiments of the present invention, an idle mobile device14 may help support uplink transmissions from a primary mobile device 14to its serving base station 12 by selectively joining a CoMP set for aprimary mobile device 14, and acting as a coordinating mobile device 14.The coordinating mobile device 14 may also support downlinktransmissions from a serving base station to a primary mobile device 14.A mobile device 14 that joins a coordinating set for a primary mobiledevice 14 is referred to herein as a cooperating mobile device 14.

For uplink transmission from the primary mobile device 14 to the servingbase station 12, a cooperating mobile device 14 receives signalstransmitted by the primary mobile device 14, and retransmits thereceived signals to the serving base station 12 for the primary mobiledevice 12. The serving base station 12 may combine the signals receivedfrom the coordinating mobile device 14 with signals received from theprimary mobile device 14 and/or other coordinating nodes for decoding.For downlink communications, a coordinating mobile device 14 receives adownlink transmission from the serving base station intended for theprimary mobile device 14, and retransmits the received signal to theprimary mobile device 14.

In the example shown in FIG. 2, UE2, which is idle, may selectively jointhe CoMP set for UE1. As a cooperating mobile device 14, UE2 may receivesignals transmitted on the uplink by UE1 and retransmit the receivedsignals to BS1. The signal transmitted from UE1 to UE2 is denoted asd₁₂. The signal transmitted from UE2 to BS1 is denoted as s₂₁. It may benoted that the signals d₁₂ and s₂₁ contain the same information as thesignal s₁₁ transmitted from UE1 to BS1. BS1 may use the received signals₂₁ along with the signal s₁₂ obtained from BS2 to help decode thesignal s₁₁. UE2 may also receive downlink transmissions from BS1intended for UE1, and retransmit the received signals to UE1. UE1 maycombine the retransmitted signal received from UE2 with the signalreceived from the serving base station for decoding.

FIG. 2 illustrates an exemplary method 50 of coordinated multipointtransmission and reception. In FIG. 2, a primary mobile device 14 (PUE)is transmitting an uplink signal to a serving base station 12. Theuplink transmission is assisted by one or more coordinating mobiledevices 14 (CUEs). The primary mobile device 14 transmits a data signalover an uplink channel to the serving base station 12 (55). Thetransmitted signal may be received by one or more cooperating mobiledevices 14. In this example, the data signal comprises a firstredundancy version (RV1) of an information signal and is transmitted ina first iteration of a HARQ process. The serving base station 12attempts to decode the received data signal. It is assumed in thisexample that decoding of the data signal fails (60). Accordingly, theserving base station 12 sends a negative acknowledgement (NACK) to theprimary mobile device 14 (65). The cooperating mobile devices 14 alsomonitor the ACK/NACK channel. In response to the NACK, the primarymobile device 14 transmits a second data signal to the serving basestation 12 (70). The second data signal comprises a second redundancyversion (RV2) of an information signal. Additionally, upon detection ofthe NACK, the cooperating mobile devices 14 retransmit the data signalreceived from the primary mobile device in the previous HARQ iteration(75). The serving base 12 combines the retransmitted data signalsreceived from the cooperating mobile devices with the data signalsreceived from the primary mobile device 14 (block 80). The combined datasignals may be used for decoding the information signal transmitted bythe primary mobile device 14.

FIG. 3 shows another exemplary method 100 of coordinated multipointtransmission and reception used to support uplink transmissions from aprimary mobile device 14 to a serving base station 12. In this method100, the primary mobile device 14 transmits a first redundancy version(RV1) of an information signal to the serving base station 12 (105). Thesignal RV1 is also received by one or more cooperating mobile devices14. Upon receipt of the signal RV1, the cooperating mobile devices 14immediately retransmit the signal RV1 to the serving base station 12 inthe same HARQ iteration (110). The serving base station 12 combines thesignals received from the cooperating mobile devices 14 and the primarymobile device 14 (115). It is assumed in this example that the decodingof the combined data signal fails (120). Accordingly, the serving basestation 12 sends a NACK to the primary mobile device (125). Thecooperating mobile devices 14 also monitor the ACK/NACK channel. Uponreceipt of the NACK, the primary mobile device 14 transmits a secondredundancy version of the information signal (RV2) to the serving basestation in a second iteration of the HARQ process (130). Upon detectionof the NACK, the cooperating mobile devices 14 may retransmit the firstredundancy version RV1 of the information signal (135). Alternatively,the cooperating mobile devices 14 may receive and retransmit the secondredundancy version (RV2) of the information signal.

FIG. 4 illustrates an exemplary method 150 according to anotherembodiment of the invention for supporting coordinated multipointtransmission and reception in downlink transmissions from a serving basestation 12 to a primary mobile device 14. During a first HARQ iteration,the serving base station 12 sends a first redundancy version (RV1) of aninformation signal to the primary mobile device 14 over a downlinkchannel (155). The downlink transmission is also received by one or morecooperating mobile devices 14. It is assumed that the primary mobiledevice 14 fails to decode the signal received from the serving basestation 12 (block 160). Accordingly, the primary mobile device 14 sendsa NACK to the serving base station (165). The cooperating mobile devices14 also monitor the ACK/NACK channel. Upon receipt of the NACK, theserving base station 12 sends a second redundancy version (RV2) of theinformation signal to the primary mobile device 14 (170). Upon detectionof the NACK, the cooperating mobile devices 14 retransmit the firstredundancy version (RV1) of the information signal to the primary mobiledevice (175). The primary mobile device 14 combines the signals receivedfrom the cooperating mobile devices 14 with the signals received fromthe serving base station 12 (180). The combined data signals may be usedto decode the information signal.

FIG. 5 illustrates another exemplary method 200 of coordinatedmultipoint transmission and reception for supporting downlinktransmissions from a serving base station 12 to a primary mobile device14. During a first HARQ iteration, the serving base station 12 sends afirst redundancy version (RV1) of an information signal to the primarymobile device 14. The downlink transmission is also received by one ormore cooperating mobile devices 14. The cooperating mobile devices 14immediately retransmit the signal RV1 to the primary mobile device 14 inthe same HARQ iteration. The primary mobile device 14 combines thesignals received from the cooperating mobile devices 14 with the signalsreceived from the serving base station (block 215) and attempts todecode the information signal. It is assumed in this example that thedecoding fails (block 220). The primary mobile device 14 sends a NACK tothe serving base station 12 (block 225). The cooperating mobile devices14 also monitor the ACK/NACK channel. Upon receipt of the NACK, theserving base station 12 sends a second redundancy version (RV2) of theinformation signal to the primary mobile device 14. The cooperatingmobile devices 14, upon detection of the NACK, also retransmit the firstredundancy version of the information signal to the primary mobiledevice 14 (block 235).Alternatively, the cooperating mobile devices 14may receive and retransmit the second redundancy version (RV2) of theinformation signal.

FIG. 6 illustrates an exemplary method 250 implemented in a cooperatingmobile device 14 for supporting coordinated multipoint transmission andreception. The cooperating mobile device 14 joins a cooperating set fora primary mobile device 14 (block 255). The decision to join acooperating set for a primary mobile device 14 may depend on a number offactors, including the link quality between the cooperating mobiledevice 14 and primary mobile device 14, and the link quality between thecooperating mobile device 14 and the serving base station 12. Otherfactors could also be taken into account. In some embodiments, thedecision to join a coordinating set for a primary mobile device 14 maybe made autonomously by the cooperating mobile device 14 based on autility function. In other embodiments, the serving base station 12 forthe primary mobile device 14 may request the cooperating mobile device14 to join a coordinating set for the primary mobile device 14. Each ofthese approaches is described in greater detail below.

After joining the coordinating set for a primary mobile device 14, thecooperating mobile device 14 receives a data signal from the primarymobile device 14 on an uplink channel, or from the serving base station12 on the downlink channel (block 260). In the case of a time divisionduplex (TDD) systems, no additional hardware is required for thecooperating mobile device 14. In frequency division duplex (FDD)systems, the cooperating mobile device 14 may need additional hardwareto receive the transmissions to or from the primary mobile device 14.The cooperating mobile device 14 may retransmit the data signal to theprimary mobile device 14 if received from the serving base station 12,or to the serving base station 12 if received from the primary mobiledevice 14 (block 270). The retransmission may involve adecode-and-forward operation. In this case, the cooperating mobiledevice 14 decodes the signal received from the serving base station 12or primary mobile device 14, re-encodes the signal, and transmits there-encoded signal. The encoding applied by the cooperating mobile device14 should be the same as the original encoding applied by either theserving base station 12 or primary mobile device 14. In otherembodiments, the cooperating mobile device 14 may function as arepeater. In this case, the signals received by the cooperating mobiledevice 14 are simply repeated without any decoding.

In some embodiments, the cooperating mobile device 14 may wait for aNACK from the receiving node before retransmitting as shown in FIGS. 2and 4. The original transmission from the sending node (primary mobiledevice 14 or serving base station 12) to the receiving node (servingbase station 12 or primary mobile device 14) may take place in a firstiteration of a HARQ process. The retransmission may take place in asecond or subsequent HARQ iteration. In other embodiments, thecooperating mobile device 14 may retransmit the signal received from thesending node immediately without waiting for a NACK. In this case, theretransmission may occur in the same iteration of the HARQ process asthe original transmission from the sending node.

FIG. 7 illustrates an exemplary method 300 implemented by a cooperatingmobile device 14 for joining the cooperating set of a primary mobiledevice 14. The cooperating mobile device 14 determines a first linkquality measurement for a communication link between the cooperatingmobile device 14 and the primary mobile device 14 (block 305). Thecooperating mobile device 14 also determines a second link qualitymeasurement for a communication link between the cooperating mobiledevice 14 and a serving base station 12 for the primary mobile device 14(block 310). The cooperating mobile device 14 then computes a utilitymetric (UM) based on the first and second link quality measurements(block 315). The cooperating mobile device 14 compares the utilitymetric to a threshold (block 320). If the utility metric is greater thanor equal to the threshold, the cooperating mobile device 14 joins thecoordinating set for the primary mobile device 14 (block 325).Otherwise, the cooperating mobile device 14 continues monitoring thefirst and second communication links.

In one exemplary embodiment, the utility metric can be based on thesignal-to-interference-plus-noise ratio (SINR) of the signal from theprimary mobile device 14 to the cooperating mobile device 14, and theSINR of the signal from the cooperating mobile device 14 to the servingbase station 12 for the primary mobile device 14. In some embodiments,the cooperating mobile device 14 may compare the SINR for eachcommunication link to the threshold and join the coordinating set ifboth SINR measurements meet or exceed the threshold. In otherembodiments, the SINR measurements for the two communication links maybe weighted and combined. In this case, the cooperating mobile device 14joins the coordinating set for the primary mobile device 14 if thecombined utility metric meets the threshold.

In some embodiments, the utility metric may incorporate factors inaddition to the SINR measurements of the communication links. As oneexample, the utility metric may take into account the additionalinterference that is attributable to the retransmission by thecooperating mobile device 14. More particularly, the cooperating mobiledevice 14 may determine a signal-to-leakage noise ratio (SLNR) due toits retransmission. The SLNR measurement may be combined with the SINRmeasurements to compute the utility metric.

FIG. 8 illustrates another exemplary method 350 implemented by acooperating mobile device 14 for selectively joining the coordinatingset of a primary mobile device 14 in the same local cluster 18. In thiscase, the selection is carried out among a plurality of mobile devices14 in a distributed and coordinated fashion. Each cooperating mobiledevice 14 in a local cluster 18 computes its own utility metric and, ifthe metric passes a threshold, transmits its utility metric to othermobile devices 14 in the local cluster 18 (block 355). The other mobiledevices 14 in the local cluster 18 do the same. Thus, the cooperatingmobile device 14 may receive utility metrics from other candidate mobiledevices 14 (block 360).

The mobile devices 14 within a local cluster 18 whose utility metricmeets the threshold requirement define a candidate set. The cooperatingmobile device 14 identifies and ranks the mobile devices 14 in thecandidate set based on the utility metrics of the mobile devices 14(block 365). The cooperating mobile device 14 then compares its rank toa predetermined number n, which represents the number of mobile devicesin a coordinating set (block 370). If the rank of the cooperating mobiledevice 14 is higher(>) than n, the cooperating mobile device 14 joinsthe coordinating set for the primary mobile device 14 (block 375).

The coordinated selection approach shown in FIG. 8 enables each of themobile devices 14 to independently determine the coordinating set forany primary mobile device 14. To minimize signaling between the mobiledevices 14, the utility metrics are transmitted only when the utilitymetrics exceed the threshold.

It will be appreciated that a given mobile device 14 in a local cluster18 may serve as a cooperating mobile device 14 for more than one othermobile device 14. In this case, the mobile device 14 computes a utilitymetric for each other mobile device 14 in the local cluster 18. As notedabove, the mobile devices 14 in the local cluster exchange the utilitymetrics. A given mobile device 14 may then join the coordinating set forone or more other mobile devices 14 in the local cluster 18, dependingon its ranking. In some embodiments, a limit may be imposed on thenumber of coordinating sets to which a given mobile device 14 may jointo prevent overloading of a single mobile device 14.

In some embodiments of the invention, the members of the coordinatingset for a given mobile device 14 may be determined by its serving basestation 12. FIG. 9 illustrates an exemplary method 400 implemented by aserving base station 12 for determining the coordinating set of aprimary mobile device 14 that is served by the base station 12. In thismethod, the base station receives link quality measurements from aplurality of candidate mobile devices 14 in the local cluster 18 of theprimary mobile device 14 (block 405). Alternatively, the serving basestation 12 may receive utility metrics from each of the candidate mobiledevices. Base stations 20 receiving link quality metrics or utilitymetrics from candidate mobile devices 14 may also exchange the receivedmetrics with other coordinating base stations 20. Based on the linkquality measurements or utility metrics, the serving base station 12selects one or more candidate mobile devices 14 to serve as cooperatingmobile devices 14 (block 410). After selecting the members of thecoordinating set, the base station sends a control signal to theselected mobile devices 14 to request that the selected mobile devices14 join the candidate set for a designated mobile device 14 (block 415).The identity of the supported mobile device 14 is included in therequest.

In some embodiments of the invention, the base station 12 may use itsknowledge of the coordinating set for a designated mobile device 14 toadapt the modulation and coding scheme (MCS) of the mobile device 14 toa more spectrally efficient value. Typically, the MCS of a given mobiledevice 14 is chosen to achieve a 90% probability of successful decodingon the first transmission, which equates to a 10% bit error rate (BER).More aggressive link adaptation implementations may target a 20% or 30%bit error rate. As known in the art, if the initial transmission is notsuccessful, the base station 12 can request retransmission by sending aNACK. When one or more cooperating mobile devices 14 are available forretransmitting the uplink signal, the probability of successful decodingwill increase. Therefore, the base station 12 can select a higher MCSvalue for the mobile device 14 when one or more cooperating mobiledevices 14 are present. In this case, the MCS for the supported mobiledevice 14 may be chosen to achieve a 90% probability of successfuldecoding based on the combined signals. This approach will result in ahigher throughput and overall improvement in spectral efficiency. Insome embodiments, the adaptation of the MCS may be used for the initialtransmission, i.e., the first HARQ iteration. In other embodiments, theMCS may be adapted in the second or subsequent HARQ iterations. Theselection of the MCS can be communicated by messaging between theprimary mobile device 14 and the cooperating mobile devices 14.

In some embodiments, the coordinating set for a primary mobile device 14may include one or more cooperating base stations 12 other than theserving base station 12 and the one or more cooperating mobile devices14. The members of the coordinating set are referred to generically ascooperating nodes. For example, the coordinating set for a primarymobile device 14 may include the serving base station 12, at least onecooperating base station 12, and at least one cooperating mobile device14. As an example, the coordinating set for UE1 in FIG. 1 may includeBS1 (the serving base station 12), BS2 (the cooperating base station12), and UE2 (the cooperating mobile device 14). BS2 may send thesignals received from UE1 over a backhaul link to BS1, while UE2retransmits the signal received from UE1 over a wireless link to BS1.BS1 may then combine the signals received from BS2 and UE2 with thesignal received directly from UE1.

FIG. 10 illustrates a wireless communication device 500 which may beused to implement the various methods herein described. Thecommunication device 500 comprises a transceiver circuit 510 and aprocessing circuit 520. The transceiver circuit 510 may operateaccording to any known wireless communication standard, such as the LongTerm Evolution (LTE) standard or WiFi standard. The processing circuit520 processes the signals transmitted and received by the transceivercircuit 510. The processing circuit 520 may comprise one or moreprocessors, microcontrollers, hardware, firmware, or a combinationthereof. The processing circuit includes a CoMP control circuit 530 forimplementing the methods and techniques herein described.

Embodiments of the invention as herein described improve the individualand aggregate throughput in a wireless communication system byexploiting idle mobile devices 14 to retransmit signals received fromother active mobile devices 14. In addition to improving capacity andthroughput, the techniques herein described will also help ineliminating coverage holes for mobile devices in poor coverage areas. Insome embodiments, the bandwidth requirements for the backhaul linksbetween the base stations, and the processing loads of the basestations, may be reduced.

Thus, the foregoing description and the accompanying drawings representnon-limiting examples of the methods and apparatus taught herein. Assuch, the present invention is not limited by the foregoing descriptionand accompanying drawings. Instead, the present invention is limitedonly by the following claims and their legal equivalents.

What is claimed is:
 1. A method implemented by a serving base station ina wireless communication network for supporting coordinated multipointtransmission and reception for a primary mobile device, comprising:receiving, by the serving base station, a first data signal transmittedby a primary mobile device; receiving, by the serving base station, asecond data signal as retransmitted by a cooperating mobile device in acoordinating set for the primary mobile device, wherein the second datasignal includes a retransmission of the first data signal; and combiningthe first and second data signals to produce a combined data signal. 2.The method of claim 1, wherein the second data signal is received in thesame subframe as the first data signal.
 3. The method of claim 1,wherein the second data signal is received in a subframe following thesubframe when the first data signal is received.
 4. The method of claim3, wherein the second data signal is received responsive to anacknowledgement signal transmitted by the serving base station to theprimary mobile device.
 5. The method of claim 1, further comprising:receiving link quality measurements from one or more candidate mobiledevices including the cooperating mobile device; computing a utilitymetric for each of the candidate mobile devices based on the linkquality measurements; and selecting the one or more candidate mobiledevices, including the cooperating mobile device, for inclusion in thecoordinating set for the primary mobile device.
 6. The method of claim5, further comprising: exchanging received link quality measurementswith one or more cooperating base stations.
 7. The method of claim 1,further comprising: adapting a modulation and coding scheme for theprimary mobile device based on a probability of decoding the combineddata signal.
 8. A base station in a wireless communication network forsupporting coordinated multipoint transmission and reception for aprimary mobile device, comprising: a transceiver circuit configured totransmit and receive signals over a wireless communication channel; anda processing circuit including a coordinated multipoint control circuitand configured to: receive a first copy of a data signal transmitted bya primary mobile device; receive a second data signal as retransmittedby a cooperating mobile device in a coordinating set for the primarymobile device; and combine the first and second data signals to producea combined data signal.
 9. The base station of claim 8, wherein thesecond data signal is received in the same subframe as the first datasignal.
 10. The base station of claim 8, wherein the second data signalis received in a subframe following the subframe when the first datasignal is received.
 11. The base station of claim 10, wherein the seconddata signal is received responsive to an acknowledgement signaltransmitted by the serving base station to the primary mobile device.12. The base station of claim 8, wherein the processing circuit isfurther configured to: receive link quality measurements from one ormore candidate mobile devices including the cooperating mobile device;compute a utility metric for each of the candidate mobile devices basedon the link quality measurements; and select the one or more candidatemobile devices, including the cooperating mobile device, for inclusionin the coordinating set for the primary mobile device.
 13. The basestation of claim 12, wherein the processing circuit is furtherconfigured to exchange link quality measurements with one or morecooperating base stations.
 14. The base station of claim 8, wherein theprocessing circuit is further configured to adapt a modulation andcoding scheme for the primary mobile device based on a probability ofdecoding the combined data signal.